I paid a visit to fellow ham and insane constructor Ian, G4EVK; who has some amazing model making equipment and a good plumbers blowtorch!
Here's some photos of the build:
I'm waiting for a "rocket" LNB that I hope will fit on the end of the waveguide (read 22mm pipe) using a compression fitting, I have also used the trick from here to check the 2.4GHz return loss - after a little bit of bending it's now looking spot on.
Yesterday I very nearly mowed the lawns, today we woke up to this:
Let it snow.....
** UPDATE **
I have used the lens from a "rocket" LNB on the front of the feed and removed the feedhorn from an Octagon LNB (with a hacksaw) and connected it all together with a 22mm compression pipe connector and some waterproofing with some silicone. I have also modified the LNB to take an external 25MHz signal (as above):
I've used the same trick I used back here to measure the return loss on 2.4 GHz and its around 20dB; I have also lashed up the receiver on the 10GHz downlink and that is working just fine.
Now, how on earth can I weather proof this?
Miss Maggie and Miss Pepper Cat seem to be economising by using the same bed? Bonkers.
I've stuck it on a dish I had lying in the hedge and attached it to an Azimuth and Elevation rotatormabob - you may remember that setup from here.
There's an LVB tracker with computer driven elevation and azimuth control.
I pointed the dish in very roughly the right part of the sky and then tuned around where I expected the signals to be, with the narrow band transponder downlink at 10489.550 - 10489.800. I've subtracted the 9750 local oscillator in the LNB.
I then found some signals and used the rotator controller to peak the signals - I've ended up at 149 degrees to the south and 18 degrees elevation - there will be many, many errors in my setup at thus time.
I'm a bit off frequency, and also drifting a touch. I need to add external frequency lock to the LNB. I've also started to setup an uplink based on the system we made here.
But I've certainly found it:
So the low beacon on the narrow band transponder is sending:
5i 5i 5i de qo-100 BK dl50amsat
and I am receiving this at a constantly drifting down frequency, currently at:
739.306 MHz on my SDR. So I add the 9750 MHz Local Oscillator and we get 10489.306 MHz
If should be between 10489.550 and 10489.555 MHz so I am a bit out of bonk and drifting.
Next job - lock the LNB to a frequency reference!
Much more to follow on this topic!
** UPDATE 1 **
I've modified my LNB to take an external 25MHz frequency - so I can feed it with a locked reference.
This has been done in accordance with the instructions here.
I'm feeding the LNB with some cheap co-ax from Amazon and I have replaced one of the "F" connectors with a BNC and attached it to my Leo Bodnar reference which I have set for 25MHz.
According to the instructions (well, read box) from the LNB:
Model: OQSLG Green HQ
Input: 10.70 GHz - 12.75 GHz
LO: 9.75 / 10.6 GHz (10.6 with 22KHz signal on coax)
0.1dB noise ratio
Gain: 60-65dB
Horizontal 18V; Vertical 12V
Now, with the 25MHz external reference, the low end beacon on the Narrow Band segment of the satellite is exactly on frequency:
I'm still worried about LNB skew as switching to horizontal doesn't null out this beacon completely = not even sure if it should, but I am definitely not seeing the DATV beacon yet so more fiddling is required.
As I fiddle, I learn. That's the basic idea anyhow.
So, I've been making a few QSOs through these amateur satellite thingamagigs.
There are a series of Japanese birds called the XW-2 series. Their frequency allocation is as follows:
Now, the number on the far left top of that image is wrong and should read 435.000.
I just had a QSO through XW-2C, the linear transponder (the bit that receives speech on the uplink and re-transmits it on the downlink) are actualy at the following frequency ranges:
Now, the observant amongst you will note that the Downlink frequency I have listed goes from high to low and the Uplink from low to high. Thats because it's a linear transponder with Spectrum Inversion. So as I tune in the 20KHz passband of the satellite I have to tune +ve in the Uplink and -ve in the downlink (or the other way round).
So when the Uplink is at 435,150, the Downlink is at 145, 815 and when Up is at 435,170 Down is at 145,795. Thats all before you add in the complexity that the Uplink is in LSB and the Downlink in USB. And then theres the further complexity of Doppler.
Now, I like to think of things very simply. If you can imagine a Sine Wave shape, with the right hand end fixed and the left hand end moving left, it is quite easy to see that the frequency is being stretched and is therefore decreasing. Similarly, if the left hand end of our imaginary sine wave was being moved to the right, the wave is being squashed and the frequency is increasing.
Therefore as the fixed point (my antenna) and the satellite (moving) get closer together the frequency that I need to tune to receive the Downlink and transmit to find the Uplink are both increasing, similarly when the bird is travelling away from me, the frequency is decreasing. The effect of this change is dependent on the actual frequency itself, so the higher the frequency the more pronounced the shift needed.
Luckily the Sat32PC software calculates the Doppler for me, but I hope the rather simplified explanation above helps explain whats actually going on.
The kit is complete and the programming of the PIC done; I had some issues with this part of the project. I couldn't get the PicProg executable as supplied as part of the fileset to function - it would appear to program OK, but the verification failed. There were way too many variables involved so I dug out the PIC programmer I purchased way back when and programmed the PIC that way. Once I had figured out all the configuration bit settings I was up and running....
The image above was taken during the calibration process. Basically the rotator control box outputs two voltages which are representative of the position of the AZ (0-360) and EL (0-180). You tell the software when the rotator is at 0 in both AZ and EL and then again when in 360 and 180. It can then calculate the appropriate voltage for anything in between.
I've chosen to use SatPC32 software for tracking the birds, controlling the rotator and also handling CAT control of the radio to automatically turn the antennas (both AZ and EL) when a selected satellite is in reach, and also control the frequency setting on the radio - including the adjustment for Doppler shift as the bird is moving towards or away from my station.
Here's a quick video of my first ever reception from an Amateur satellite. This is before getting the CAT control functional - just the antennas are moving automatically to track the bird as it passes:
And here is a quick video showing the auto tuning for Doppler (no sound):
So now it's time to do some research and some listening before I decide which satellite and how to make my first QSO. Fun egh?
Here's Miss Luna Cat asleep behind one of my monitors:
For quite some time I have wanted to try my hand at Amateur Satellites. Now, I plan to utilise my IC-9100 for this task - it is a full duplex radio meaning I can TX on one band whilst RX on the other.
I decided I would build myself a "proper" satellite tracking antennamabob, and here it is up in the air:
There's 3 elements on 144Mhz and 7 elements on 70cm. The antenna has both azimuth and elevation rotation capabilities using one of these:
It's a Yaesu G-5500 rotator; unfortunately they don't supply the necessary hardware to separate the azimuth and elevation rotators - so I had to fabricate something suitable. I've mounted the azimuth rotator way down the pole and utilising these brackets from Barenco and a Yaesu thrust bearing we have a suitable working arrangement with minimum weight at the top.
The plan is to develop a means of automatically controlling the antennas such that they will auto track satellites using PC based software. I've bought one of these kits from AMSAT, here in early construction:
